The present invention relates to a fuel injection nozzle for use in a diesel engine, the fuel injection nozzle having a timing sensor for electrically detecting the timing of injection of fuel into the diesel engine based on operation of the fuel injection nozzle.
There are known fuel injection nozzles for use in diesel engines, having a pressure sensor mounted in a nozzle holder for detecting the pressure from a needle valve when it is opened for fuel injection. The timing of fuel injection can be detected by detecting an output signal from the pressure sensor. Another known timing sensor is arranged to detect the timing of fuel injection by detecting an electric resistance between the needle valve and the nozzle holder.
One example of such a pressure sensor comprises a piezoelectric element as disclosed in Japanese Laid-Open patent Publication No. 56-113044 published on Sept. 5, 1981. According to the disclosed arrangement, a terminal rod made of an electrically conductive material is supported, with an oil seal and electric insulation, in a nozzle holder end remote from the needle valve in the fuel injection nozzle. When the needle valve is lifted off its seat, it applies a pressure to the piezoelectric element which then issues an output signal through the terminal rod. The piezoelectric element is grounded through a circular grounding plate having on its outer peripheral edge a plurality of teeth or projections angularly spaced at equal intervals and projecting radially outwardly into contact with the inner wall surface of a spring chamber defined in the nozzle holder. The teeth of the grounding plate are held in resilient engagement with the nozzle holder for grounding the piezoelectric element. The grounding plate is interposed between the piezoelectric element and the upper end surface of a spring disposed in the spring chamber.
A timing sensor which detects the electric resistance between the needle valve and the nozzle holder is revealed in Japanese patent Publication No. 55-50188, for example, published on Dec. 16, 1980. Electric switching effected between the needle valve and the nozzle holder when the needle valve is opened and closed results in different electric resistances on opening and closing of the needle valve. An electrically insulating plate and an electrically conductive contact plate are disposed between a spring seat and the nozzle holder, with a lead wire extending from the contact plate for detecting the electric resistance.
The piezoelectric pressure sensor is tedious and time-consuming to assemble since the terminal rod has to be inserted through the nozzle holder. Although the grounding plate ensures good electric contact with the nozzle holder, it cannot be easily assembled in place or may be tilted when assembled, thus resulting in a laborious process of grounding the piezoelectric element. It has not been possible to insert preassembled pressure sensor parts into the nozzle holder. The prior timing sensor for detecting the electric resistance is also disadvantageous in that it is tedious and time-consuming to assemble the insulating plate and the contact plate and to draw the lead wire from the contact plate. The insulating plate and the contact plate cannot be inserted in preassembled condition in the nozzle holder.